Lipid phases of biogenic origin contain not only the neutral fats sought after for further use, such as triglycerides for example, but also in most cases numerous organic accompanying substances which, in the biological context from which the lipids originate, ensure solubilization. Therefore, despite their altogether amphiphilic properties, said accompanying substances frequently have a noticeably large lipophilicity. This depends on the ratio of hydrophilic and hydrophobic molecular parts. Whereas compounds having a large water-molecule binding capacity, as is the case for the hydratable phospholipids (phosphatidylcholine and phosphatidyl-ethanolamine) for example, can be easily washed out by an introduction of water into a lipid phase, the same cannot be said for the structurally very similar phospholipids referred to as nonhydratable (phosphatidylinositols and phosphatidylserine). Furthermore, most lipid phases also contain glycolipids and glycoglycerolipids, which frequently have fatty acid residues having very long chains and, despite the presence of polar groups, cannot be easily flushed out of a lipid mixture by means of an aqueous medium. Furthermore, most lipid phases of plant origin also contain sterol glycosides and also hydrophobic dyes such as carotenes and chlorophylls. Such compounds are completely water-insoluble and therefore remain in the lipid phase during an aqueous refining process. Nevertheless, all the aforementioned compounds are capable of binding low amounts of water molecules via electrostatic interaction forces, for example to OH groups. Furthermore, the aforementioned compounds are usually present together in complex structures, with the inclusion of ions from the group of the alkaline earth metals and of the metals. This further increases the cohesion in the region of hydrophilic groups. This explains why it is necessary to purify such lipid mixtures using aqueous media containing strong bases and strong acids. Nevertheless, it has so far not been possible to demonstrate for any method that a complete removal of compounds which can bind water ions via OH groups is possible. As a result, it is consequently also not possible, by means of simple aqueous refining techniques, to lower the residual water content or the water uptake capacity of the refined oil to an extent that satisfies the product requirements for food quality as well as for a lipid phase used as technical product, for example for biogenic fuels. Drying of aqueously refined lipid mixtures according to the prior art is achieved by clearing the pretreated lipid phases of water fractions situated therein by either heating or a vacuum-drying process, it being realistically possible to achieve a reduction in the residual water content to values between 0.05 and 0.15% by weight. Such a drying process increases the refining costs. Furthermore, the water-binding compounds remain in the lipid phase, and so, in the event of a repeated introduction of water, there can be a reoccurrence of water binding and thus turbidity of the lipid phase. Therefore, said compounds are sometimes also referred to as turbidity-inducing agents, and, in this connection, a turbidity owing to what is understood here to mean turbidity-inducing agents does not become visible as a result of complex organic compounds themselves becoming visible; instead, the turbidity arises owing to water molecules which are bound by said organic compounds. In contrast to complex organic structures which are likewise referred to as turbidity-inducing agent and which can be imaged by means of optical techniques and, as corpuscular structures, are therefore also extractable and removable by means of a filtration, the turbidity-inducing agents referred to here are characterized in that they cannot be removed by means of a filter technique based on a size exclusion of corpuscular particles.
The presence of such organic compounds can also adversely affect the oxidation stability of the lipid phases in which they are situated. Therefore, their removal from a lipid phase is desirable, since this yields a distinctly improved refinement product. The refining steps downstream, according to the prior art, of an aqueous refining of triglyceride mixtures, such as a treatment with fuller's earth and/or a vapor treatment (deodorization), are capable of distinctly reducing the water-binding capacity of aqueously prerefined lipid phases. A disadvantage here is that the process steps following the aqueous refining steps lead to a considerable increase in the production costs. Furthermore, a treatment with fuller's earth also leads to a relevant loss of triglycerides, which are removed thereby.
An aqueous refining method has now been established, by means of which a distinctly more efficient removal of amphiphilic accompanying substances from a lipid phase is possible. Here, it is possible to remove very efficiently both amphiphilic compounds containing, for example, saccharides, such as glycolipids from lipid phases, and carboxylic acids. Furthermore, there is also a relevant removal of dyes, achieving, for example, a quality for such a refined oil which no longer necessitates a further treatment with a fuller's earth or a deodorization. This allows an efficient and cost-effective aqueous refining of biogenic lipid phases, making it possible to save process costs. However, it has become apparent that, specifically in the case of very complete removal of glycolipids, free fatty acids, phosphorus-containing compounds and alkaline earth metal ions, the refined lipid phases which are obtained after a centrifugal removal of these compounds together with the aqueous phases still have a distinct turbidity. In this case, there were amounts of water residual content of >1.5% by weight, and so the oils did not attain the required product specification, although a depletion of the phosphorus content to values of <2 ppm and of the content of calcium, magnesium and iron to values of <0.05 ppm and of the content of free fatty acids of <0.15% by weight had been achieved. When such a refined turbid oil phase was subjected to a drying process, for example by means of a vacuum-drying process, it was possible to reduce the residual moisture content to <0.1% by weight. The dried oils were transparent. By mixing with water, relevant amounts of water could be introduced into such oils, and so said oils became turbid again and could not be clarified by centrifugal process technologies. A reduction in the residual moisture of a refined lipid phase is desired in order to obtain an extremely clear oil; however, the residual moisture is also a crucial determinant for the improvement of the quality of the oil. Another aspect of a residual moisture of a lipid phase concerns storage stability, which is adversely affected by a relatively high content of water molecules remaining in a lipid phase. However, this also occurs when the lipid phase contains compounds which can bind water molecules, for example from the air. Therefore, it is necessary to reduce the residual water content to a product-specific minimum and desirable to eliminate organic compounds which promote an uptake of water into the lipid phase. In lipid phases and especially in oils and fats of plant or animal origin, there are chemical reactions which occur to a variable extent dependent on the storage conditions (air/light exposure, temperature conditions, container surfaces) and also on the presence of compounds which can bring about an oxidation of carbon double bonds (see p-anisidine value determination embodiments), and on the presence of compounds which allow a binding or reduction of free radicals, such as tocopherols, polyphenols or squalenes. The oxidative processes can give rise to, inter alia, aldehydes, ketones and free fatty acids, which further quicken the oxidative processes and are largely responsible for off-flavors in plant oils. During a classic refining method, the degumming method generally leads to a reduction in compounds which cause oxidative processes. The treatment of oils with fuller's earth can lead to acid-catalyzed oxidations; furthermore, compounds having antioxidative properties are depleted in this case to a varying extent, and so this method step can distinctly worsen the oxidation stability of an oil. In principle, the same applies to the deodorization process, especially when relatively high vapor temperatures (>220° C.) and a relatively long residence time (>15 minutes) of the oil are required. Therefore, storage stability is affected to a varying extent by the classic methods. In comparison to cold-pressed oils, such refined oils therefore frequently have no advantage with respect to storage stability, since, in the native oils, the antioxidants situated therein were left and no compounds which promote an autoxidation were added. Substances which promote an autoxidation usually have free-radical or free-radical-forming groups, or have a binding capacity for water molecules. A specific depletion of these compounds is not possible according to the prior art.
It has been possible to show that water extraction methods, such as a vacuum-drying process, lead to the desired removal of the residual water contents. However, the use of these techniques makes the aqueous refining method uneconomical. Furthermore, a repeated introduction of water into a lipid phase which had been aqueously refined and then treated by means of vacuum drying is still possible. This considerably impairs the product properties of the lipid phases. Since accompanying substances were already depleted in said lipid phases to an extent which no longer necessitates further refining steps, such as a bleaching or deodorization, and in order to clear the thus obtained lipid phases of the turbidity-inducing agents still present in an economical manner and a manner gentle to the product and thus, firstly, to reduce the residual water content to the required extent and, secondly, to reduce the ability of water to be introduced again, a new method was required. Surprisingly, a very simple and effective method has now been found, which, for such a well prepurified but turbid lipid phase, allows a removal of the residual content of water from a lipid phase which can be obtained following an aqueous refining process and, at the same time, also removes the turbidity-inducing agents responsible therefor. Furthermore, since the method can be carried out with comparatively inexpensive compounds at ambient temperatures and without relevant apparatus expenditure, with simultaneously only very low to completely negligible loss of neutral lipids, said method represents a considerable improvement in relation to the above-described methods from the prior art and satisfies the desired conditions. It is therefore an object of the present invention to provide methods for drying lipid phases with simultaneous removal of water-binding organic turbidity-inducing agents.